This application claims the benefit of Korean Patent Application Nos. 00-26177 and 00-34505, filed May 16, 2000 and Jun. 22, 2000, respectively, in the Korean Industrial Property Office, the disclosures of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a polymeric gel electrolyte and a lithium battery employing the same, and more particularly, to a polymeric gel electrolyte free from leakage of an electrolytic solution even at an increase in the capacity, and a lithium battery having improved safety and reliability by using the polymeric gel electrolyte.
2. Description of the Related Art
In a conventional cylindrical or prismatic lithium secondary ion battery, a polyethylene separator is generally used in consideration of short-circuit prevention and a thermal-shut-down effect as well as tolerance against tension applied when winding an electrode assembly having a cathode, an anode and a separator interposed therebetween. However, in the case of using the polyethylene separator, it is quite difficult to manufacture a high-capacity battery of over 1000 mAh, in practice, due to leakage of an electrolytic solution.
As it was known that use of an ethylene oxide homopolymer and alkali metallic ion system makes it possible to obtain excellent ion conductivity characteristics of a battery, research into solid polymer electrolyte has been intensively conducted. As a result, much attention has been paid to polyether such as polyethylene oxide as a polymer matrix, in view of its high mobility and solubility of metallic cations.
Movement of metallic ions occurs at an amorphous area rather than at a crystallized area of polymer. Thus, in order to reduce the crystallinity of polyethylene oxide, the polyethylene oxide may be copolymerized with various kinds of epoxides, as proposed in U.S. Pat. Nos. 5,968,681 and 5,837,157.
In order to solve a serious problem of leakage of an electrolytic solution during manufacture of a high-capacity battery having a winding-type electrode assembly, the present inventors completed a battery according to the present invention to overcome the disadvantages of a polyethylene separator, by using a separator formed of a crosslinked structure of polyethylene oxide, together with the polyethylene separator.
To solve the above problems, it is a first object of the present invention to provide a polymeric electrolyte which can prevent leakage of an electrolytic solution due to an increase in battery capacity.
It is a second object of the present invention to provide a lithium battery having improved reliability and safety by using the electrolyte.
To achieve the first object, there is provided a polymeric gel electrolyte comprising a lithium salt, an organic solvent and a curing product of a composition having a terpolymer having a repeating unit represented by formula (1), a repeating unit represented by formula (2) and a repeating unit represented by formula (3): 
wherein n is an integer from 1 to 12, and R is a C1 to C12 alkyl group.
A plasticizer is further added to the composition.
According to another aspect of the present invention, there is provided a polymeric gel electrolyte comprising a lithium salt, an organic solvent and a polymerizing product of a crosslinking agent and a terpolymer having a repeating unit represented by formula (1), a repeating unit represented by formula (2) and a repeating unit represented by formula (3): 
wherein n is an integer from 1 to 12, and R is a C1 to C12 alkyl group.
N,N-(1,4-phenylene) bismaleimide is preferably used as the crosslinking agent and the content thereof is 0.1 to 50 parts by weight based on 100 parts by weight of the terpolymer.
A catalyst is further included in the polymerization reaction between the terpolymer and the crosslinking agent. Preferred examples of the catalyst include benzoylperoxide, azobis(isobutyronitrile) (AIBN) and dicumylperoxide, and the content of the catalyst is 0.1 to 20 parts by weight based on 100 parts by weight of the terpolymer.
To achieve the second object, there is provided a lithium battery including an electrode assembly having a cathode, an anode and a separator interposed therebetween, a polymeric gel electrolyte comprising a lithium salt, an organic solvent and a curing product of a composition having a terpolymer having a repeating unit represented by formula (1), a repeating unit represented by formula (2) and a repeating unit represented by formula (3): 
wherein n is an integer from 1 to 12, and R is a C1 to C12 alkyl group, and a case accommodating the electrode assembly and the polymeric electrolyte.
Alternatively, the present invention provides a lithium battery including an electrode assembly having a cathode, an anode and a separator interposed therebetween, a polymeric gel electrolyte comprising a lithium salt, an organic solvent and a polymerizing product of a crosslinking agent and a terpolymer having a repeating unit represented by formula (1), a repeating unit represented by formula (2) and a repeating unit represented by formula (3): 
wherein n is an integer from 1 to 12, and R is a C1 to C12 alkyl group, and a case accommodating the electrode assembly and the polymeric electrolyte.
The polymeric electrolyte is preferably prepared by mixing the terpolymer having the repeating unit represented by formula (1), the repeating unit represented by formula (2), and the repeating unit represented by formula (3) with a lithium salt, an organic solvent, a catalyst and a crosslinking agent, injecting the resultant into a case accommodating the electrode assembly, and polymerizing. Alternatively, the polymeric electrolyte may be prepared by coating a composition obtained by mixing the terpolymer having the repeating unit represented by formula (1), the repeating unit represented by formula (2), and the repeating unit represented by formula (3) with a lithium salt, an organic solvent, a catalyst and a crosslinking agent, on at least one of a cathode, an anode and a separator, drying the resultant and polymerizing.